Method for operating a high sensitivity active pixel

1. A method comprising: allowing light to be incident upon a photodetector circuit to thereby generate an input signal representing the light, the input signal being applied to a gate of a first field effect transistor (FET); applying a first control signal to a drain of the first FET and thereby generating an output current at a source of the first FET; and accumulating charge in a capacitor coupled to the source of the first FET.

2. The method of claim 1 wherein the first control signal is a digital pulse.

3. The method of claim 2 further comprising: capturing a signal value related to a voltage across the capacitor while the digital pulse is asserted.

4. The method of claim 1 further comprising: asserting a second control signal, that is the complement of the first control signal, to reset the photodetector circuit; and capturing a reset value related to a voltage across the capacitor immediately after deasserting the second control signal.

5. The method of claim 4 wherein the second control signal is applied to a drain of a reset FET coupled to a photodiode in the photodetector circuit.

6. The method of claim 3 further comprising: asserting a select signal at a gate of a second FET having a drain coupled to the capacitor through a source follower, to provide a current representative of the voltage across the capacitor.

7. The method of claim 6 further comprising: raising the voltage at a gate of the source follower in response to the select signal being asserted.

8. The method of claim 7 wherein the voltage at the gate of the source follower is raised by at least one threshold voltage (V t ) in response to the select signal being asserted.

9. The method of claim 3 further comprising: converting the captured signal value into digital format representing part of a digital image; and transferring the digital captured signal value to a personal computer.